Plasma grid implant system for use in solar cell fabrications

ABSTRACT

A method of ion implantation comprising: providing a plasma within a plasma region of a chamber; positively biasing a first grid plate, wherein the first grid plate comprises a plurality of apertures; negatively biasing a second grid plate, wherein the second grid plate comprises a plurality of apertures; flowing ions from the plasma in the plasma region through the apertures in the positively-biased first grid plate; flowing at least a portion of the ions that flowed through the apertures in the positively-biased first grid plate through the apertures in the negatively-biased second grid plate; and implanting a substrate with at least a portion of the ions that flowed through the apertures in the negatively-biased second grid plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. ProvisionalApplication Ser. No. 61/219,379, filed Jun. 23, 2009, entitled “PLASMAGRID IMPLANT SYSTEM FOR USE IN SOLAR CELL FABRICATIONS,” which is herebyincorporated by reference in its entirety as if set forth herein.

FIELD OF THE INVENTION

The present invention relates generally to the field of solar cells andother large substrate implant applications. More particularly, thepresent invention relates to solar cell devices and methods of theirformation.

BACKGROUND OF THE INVENTION

Although traditional beamline implantation of wafers can provide highpower density, it has several disadvantages. For example, it onlyprovides a single beamlet. Additionally, it uses a lot of power in asmall beam spot, and the wafer gets quite hot. As a result, productivityis low.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a plasma grid implantationsystem is provided. The system comprises: a plasma source configured toprovide plasma; a first grid plate comprising a plurality of aperturesconfigured to allow ions from the plasma in a plasma region to passtherethrough, wherein the first grid plate is configured to bepositively biased, either continuously in DC mode or in pulsed mode, bya power supply; a second grid plate comprising a plurality of aperturesconfigured to allow the ions to pass therethrough subsequent to the ionspassing through the first grid plate, wherein the second grid plate isconfigured to be negatively biased, either continuously in DC mode or inpulsed mode, by a power supply; and a substrate holder configured tosupport a substrate in a position where the substrate is implanted withthe ions subsequent to the ions passing through the second grid plate.

In some embodiments, the position of at least one of the first gridplate, the second grid plate, and the substrate holder is configured tobe adjusted between a homogeneous implantation position and a selectiveimplantation position, the homogeneous implantation position isconfigured to enable a single laterally-homogeneous ion implantationacross the substrate on the substrate holder, wherein the singlelaterally-homogeneous ion implantation is formed from a combination ofions that have passed through different apertures of the second gridplate, and the selective implantation position is configured to enable aplurality of laterally spaced-apart ion implantations of the substrateon the substrate holder, wherein the plurality of laterally spaced-apartion implantations is formed from ions that have passed through thedifferent apertures of the second grid plate.

In some embodiments, the system further comprises a third grid platedisposed between the second grid plate and the substrate holder, and thethird grid plate comprises a plurality of apertures configured to allowthe ions to pass therethrough subsequent to the ions passing through thesecond grid plate. In some embodiments, the third grid plate isgrounded. In some embodiments, the position of at least one of the thirdgrid plate and the substrate holder is configured to be adjusted betweena homogeneous implantation position and a selective implantationposition, the homogeneous implantation position configured to enable asingle laterally-homogeneous ion implantation across the substrate onthe substrate holder, wherein the single laterally-homogeneous ionimplantation is formed from a combination of ions that have passedthrough different apertures of the second grid plate, and the selectiveimplantation position configured to enable a plurality of laterallyspaced-apart ion implantations of the substrate on the substrate holder,wherein the plurality of laterally spaced-apart ion implantations isformed from ions that have passed through the different apertures of thesecond grid plate.

In some embodiments, the apertures of at least one of the first gridplate and the second grid plate are substantially circular holes. Insome embodiments, the apertures of at least one of the first grid plateand the second grid plate are elongated slots. In some embodiments, eachone of the apertures of at least one of the first grid plate and thesecond grid plate comprises a top end and a bottom end, wherein thebottom end is closer to the substrate holder than the top end, andwherein the diameter of each aperture gradually increases from the topend to the bottom end.

In some embodiments, the first grid plate and the second grid platecomprise a material chosen from the group consisting of: silicon,graphite, silicon carbide, and tungsten. In some embodiments, the systemfurther comprises a chamber defined by chamber walls, wherein the plasmaregion, the first grid plate, and the second grid plate are housedwithin the chamber, and wherein the chamber walls are configured torepel ions in the plasma region using a magnetic field. In someembodiments, one or more magnets are coupled to the chamber walls.

In another aspect of the present invention, a method of ion implantationis provided. The method comprises: providing a plasma within a plasmaregion of a chamber; positively biasing a first grid plate, wherein thefirst grid plate comprises a plurality of apertures and is disposed in afirst position; negatively biasing a second grid plate, wherein thesecond grid plate comprises a plurality of apertures and is disposed ina first position; flowing ions from the plasma in the plasma regionthrough the apertures in the positively-biased first grid plate; flowingat least a portion of the ions that flowed through the apertures in thepositively-biased first grid plate through the apertures in thenegatively-biased second grid plate; and implanting a substrate with atleast a portion of the ions that flowed through the apertures in thenegatively-biased second grid plate, wherein the substrate is disposedin a first position.

In some embodiments, a shadow mask comprising a plurality of openingsformed therethrough is disposed a predetermined distance away from thesubstrate, and the method further comprises flowing at least a portionof the ions that flowed through the apertures in the negatively-biasedsecond grid plate through the openings in the shadow mask beforeimplanting the substrate.

In some embodiments, a photoresist mask comprising a plurality ofopenings formed therethrough is placed in contact with the substrate,and the method further comprises flowing at least a portion of the ionsthat flowed through the apertures in the negatively-biased second gridplate through the openings in the photoresist mask before implanting thesubstrate.

In some embodiments, the method further comprises: adjusting theposition of at least one of the first grid plate, second grid plate, andthe substrate holder to a second position; providing a plasma within theplasma region subsequent to the adjustment to the second position;flowing ions from the plasma in the plasma region through the aperturesin the positively-biased first grid plate subsequent to adjustment tothe second position; flowing at least a portion of the ions that flowedthrough the apertures in the positively-biased first grid plate throughthe apertures in the negatively-biased second grid plate subsequent toadjustment to the second position; and implanting a substrate with atleast a portion of the ions that flowed through the apertures in thenegatively-biased second grid plate subsequent to adjustment to thesecond position, wherein the implantation performed when the at leastone of the first grid plate, second grid plate, and the substrate holderwas in the first position forms a single laterally-homogeneous ionimplantation across the substrate, wherein the singlelaterally-homogeneous ion implantation is formed from a combination ofions that have passed through different apertures of the second gridplate, and wherein the implantation performed when the at least one ofthe first grid plate, second grid plate, and the substrate holder was inthe second position forms a plurality of laterally spaced-apart ionimplantations of the substrate, wherein the plurality of laterallyspaced-apart ion implantations is formed from ions that have passedthrough the different apertures of the second grid plate.

In some embodiments, a third grid plate is disposed between the secondgrid plate and the substrate, the third grid plate is disposed in afirst position and comprises a plurality of apertures configured toallow the ions to pass therethrough subsequent to the ions passingthrough the second grid plate. In some embodiments, the third grid plateis grounded. In some embodiments, the method further comprises:adjusting the position of at least one of the first grid plate, secondgrid plate, the third grid plate, and the substrate holder to a secondposition; providing a plasma within the plasma region subsequent to theadjustment to the second position; flowing ions from the plasma in theplasma region through the apertures in the positively-biased first gridplate subsequent to adjustment to the second position; flowing at leasta portion of the ions that flowed through the apertures in thepositively-biased first grid plate through the apertures in thenegatively-biased second grid plate subsequent to adjustment to thesecond position; flowing at least a portion of the ions that flowedthrough the apertures in the negatively-biased second grid plate throughthe apertures in the third grid plate subsequent to adjustment to thesecond position; and implanting a substrate with at least a portion ofthe ions that flowed through the apertures in the third grid platesubsequent to adjustment to the second position, wherein theimplantation performed when the at least one of the first grid plate,second grid plate, the third grid plate, and the substrate holder was inthe first position forms a single laterally-homogeneous ion implantationacross the substrate, wherein the single laterally-homogeneous ionimplantation is formed from a combination of ions that have passedthrough different apertures of the third grid plate, and wherein theimplantation performed when the at least one of the first grid plate,second grid plate, the third grid plate, and the substrate holder was inthe second position forms a plurality of laterally spaced-apart ionimplantations of the substrate, wherein the plurality of laterallyspaced-apart ion implantations is formed from ions that have passedthrough the different apertures of the third grid plate.

In some embodiments, the apertures of at least one of the first gridplate and the second grid plate are substantially circular holes. Insome embodiments, the apertures of at least one of the first grid plateand the second grid plate are elongated slots. In some embodiments, eachone of the apertures of at least one of the first grid plate and thesecond grid plate comprises a top end and a bottom end, wherein thebottom end is closer to the substrate holder than the top end, andwherein the diameter of each aperture gradually increases from the topend to the bottom end.

In some embodiments, the first grid plate and the second grid platecomprise a material chosen from the group consisting of: silicon,graphite, silicon carbide, and tungsten. In some embodiments, the plasmaregion, the first grid plate, and the second grid plate are housedwithin a chamber that is defined by chamber walls, and wherein thechamber walls are configured to repel ions in the plasma region using anelectric field.

In some embodiments, the method further comprises the step of applying apulsed voltage to the plasma. In some embodiments, the method furthercomprises the step of applying a pulsed voltage to the substrate. Insome embodiments, the pulsed voltage is directed towards a plurality ofdifferent locations on the substrate.

In some embodiments, the method further comprises: passing the substratethrough a first plurality of differentially-pumped stages prior to thesubstrate being implanted with the ions, wherein each stage in the firstplurality of differentially-pumped stages comprises a lower pressurethan the previous stage in the first plurality of differentially-pumpedstages; passing the substrate from the first plurality of differentiallypumped stages directly to an implantation stage; passing the substratefrom the implantation stage directly to a second plurality ofdifferentially-pumped stages subsequent to the substrate being implantedwith the ions, and passing the substrate through the second plurality ofdifferentially-pumped stages, wherein each stage in the second pluralityof differentially-pumped stages comprises a higher pressure than theprevious stage in the second plurality of differentially-pumped stages,wherein the implantation stage comprises a lower pressure than any ofthe stages in the first plurality and second plurality ofdifferentially-pumped stages.

In yet another aspect of the present invention, a plasma gridimplantation system is provided. The system comprises: a plasma sourceconfigured to provide plasma; a grid assembly comprising a plurality ofgrid plates, wherein each grid plate comprises a plurality of aperturesconfigured to allow ions from the plasma to pass therethrough; and asubstrate holder configured to support a substrate in a position wherethe substrate is implanted with the ions subsequent to the ions passingthrough the plurality of apertures of the grid plates, wherein at leastone of the substrate holder and the grid plates is configured to beadjusted between a homogeneous implantation position and a selectiveimplantation position, wherein the homogeneous implantation position isconfigured to enable a single laterally-homogeneous ion implantationacross the substrate on the substrate holder, the singlelaterally-homogeneous ion implantation being formed from a combinationof ions that have passed through different apertures of the second gridplate, and wherein the selective implantation position is configured toenable a plurality of laterally spaced-apart ion implantations of thesubstrate on the substrate holder, the plurality of laterallyspaced-apart ion implantations is formed from ions that have passedthrough the different apertures of the second grid plate.

In some embodiments, the plurality of grid plates comprises: a firstgrid plate comprising a plurality of apertures configured to allow ionsfrom the plasma in a plasma region to pass therethrough; and a secondgrid plate comprising a plurality of apertures configured to allow theions to pass therethrough subsequent to the ions passing through thefirst grid plate. In some embodiments, the first grid plate isconfigured to be positively-biased by a power supply. In someembodiments, the second grid plate is configured to be negatively-biasedby a power supply. In some embodiments, the plurality of grid platesfurther comprises a third grid plate comprising a plurality of aperturesconfigured to allow the ions to pass therethrough subsequent to the ionspassing through the second grid plate. In some embodiments, the thirdgrid plate is configured to be grounded. In some embodiments, the firstgrid plate, the second grid plate, and the substrate holder are allconfigured to have their positions adjusted.

In yet another aspect of the present invention, a method of ionimplantation is provided. The method comprises: providing a plasmawithin a plasma region of a chamber; providing a grid assemblycomprising a plurality of grid plates, wherein each grid plate comprisesa plurality of apertures; flowing a first set of ions from the plasma inthe plasma region through the apertures in each of the grid plates inthe grid assembly while each of the grid plates is in a first position;homogeneously implanting a substrate with at least a portion of thefirst set of ions that flowed through the apertures in the grid plateswhile the substrate is supported in a first position by a substrateholder, thereby forming a single laterally-homogeneous ion implantationacross the substrate from a combination of the first set of ions thathave passed through different apertures of the same grid plate;adjusting the position of the substrate or at least one of the gridplates to a second position; flowing a second set of ions from theplasma in the plasma region through the apertures in each of the gridplates in the grid assembly subsequent to the adjustment to the secondposition; selectively implanting the substrate with at least a portionof the second set of ions that flowed through the apertures in the gridplates subsequent to the adjustment to the second position, therebyforming a plurality of laterally spaced-apart ion implantations on thesubstrate from a portion of the second set of ions that have passedthrough different apertures of the same grid plate.

In some embodiments, the adjusting step comprises adjusting the positionof the substrate. In some embodiments, adjusting the position of thesubstrate comprises moving the substrate closer to the grid assembly.

In some embodiments, the adjusting step comprises adjusting the positionof one of the grid plates. In some embodiments, adjusting the positionof one of the grid plates comprises moving one of the grid plates closerto the substrate.

In some embodiments, the plurality of grid plates comprises a first gridplate and a second grid plate, the first grid plate beingpositively-biased, and the second grid plate being negatively biased. Insome embodiments, the plurality of grid plates further comprises a thirdgrid plate that is grounded.

In yet another aspect of the present invention, a method of ionimplantation is provided. The method comprises: providing a first singletype of dopant material to a plasma generator; the plasma generatorbreaking up the first single type of dopant material into a firstplurality of dopant species; and implanting a substrate with the firstplurality of dopant species.

In some embodiments, the substrate is implanted with the first pluralityof dopant species in a single implantation step. In some embodiments,each one of the dopant species is implanted into the substrate at adifferent depth. In some embodiments, the first single type of dopantmaterial is phosphine. In some embodiments, the first plurality ofdopant species comprises P³⁰ , P⁻⁻, P⁺⁺⁺, P₂ ⁺, P₃ ⁺, and P₅ ⁺. In someembodiments, the first single type of dopant material is boron orarsenic.

In some embodiments, a combination of different types of dopant materialis used to implant different pluralities of dopant species. In someembodiments, the different types of dopant material can be provided inprecursor form as gasses, liquids, solids, or any combination thereof.

In some embodiments, a second single type of dopant material is providedto the plasma generator, the plasma generator breaks up the secondsingle type of dopant material into a second plurality of dopant speciesduring the same period that the plasma generator breaks up the firstsingle type of dopant material into the first plurality of dopantspecies, and the second plurality of dopant species is implanted intothe substrate during the same period that the first plurality of dopantspecies is implanted into the substrate. In some embodiments, the firstsingle type of dopant material and the second single type of dopantmaterial are each a precursor gas. In some embodiments, the first singletype of dopant material is arsine and the second single type of dopantmaterial is phosphine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional side view of one embodiment of ahomogeneously doped solar cell in accordance with the principles of thepresent invention.

FIGS. 2A-2C illustrate cross-sectional side views of different ways ofselectively implanting a solar cell in accordance with the principles ofthe present invention.

FIG. 3 illustrates a cross-sectional side view of one embodiment of asolar cell with contact gridlines in accordance with the principles ofthe present invention.

FIG. 4 illustrates one embodiment of a plasma immersion implantationsystem in accordance with the principles of the present invention.

FIG. 5 illustrates a cross-sectional side view of one embodiment of asolar cell with a homogeneous implant in accordance with the principlesof the present invention.

FIG. 6 illustrates a cross-sectional side view of another embodiment ofa solar cell with homogeneous and selective implants in accordance withthe principles of the present invention.

FIG. 7 illustrates a cross-sectional side view of one embodiment of aplasma grid implant system in accordance with the principles of thepresent invention.

FIG. 8 illustrates a cross-sectional 3-dimensional perspective view ofanother embodiment of a plasma grid implant system in accordance withthe principles of the present invention.

FIGS. 9A-9B illustrate cross-sectional side views of different gridplate apertures in accordance with the principles of the presentinvention.

FIG. 10 illustrates a cross-sectional side view of one embodiment ofplasma ions passing through grid plates in accordance with theprinciples of the present invention.

FIGS. 11A-11B illustrate plan views of different grid plate apertures inaccordance with the principles of the present invention.

FIG. 12 illustrates a plan view of one embodiment of a load-lockedimplantation system in accordance with the principles of the presentinvention.

FIG. 13 illustrates a cross-sectional view of one embodiment of amulti-stage differentially pumped implantation system in accordance withthe principles of the present invention.

FIG. 14 illustrates a process flow diagram of one embodiment of a methodof ion implantation in accordance with the principles of the presentinvention.

FIG. 15 illustrates a process flow diagram of another embodiment of amethod of ion implantation in accordance with the principles of thepresent invention.

FIG. 16 illustrates a process flow diagram of yet another embodiment ofa method of ion implantation in accordance with the principles of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable one of ordinary skillin the art to make and use the invention and is provided in the contextof a patent application and its requirements. Various modifications tothe described embodiments will be readily apparent to those skilled inthe art and the generic principles herein may be applied to otherembodiments. Thus, the present invention is not intended to be limitedto the embodiment shown but is to be accorded the widest scopeconsistent with the principles and features described herein.

Furthermore, it is contemplated that any features from any embodimentcan be combined with any features from any other embodiment. In thisfashion, hybrid configurations of the illustrated embodiments are wellwithin the scope of the present invention.

Various aspects of the disclosure may be described through the use offlowcharts. Often, a single instance of an aspect of the presentdisclosure may be shown. As is appreciated by those of ordinary skill inthe art, however, the protocols, processes, and procedures describedherein may be repeated continuously or as often as necessary to satisfythe needs described herein. Additionally, it is contemplated that methodsteps can be performed in a different order than the order illustratedin the figures, unless otherwise disclosed explicitly or implicitly.

The present invention is directed towards an implant system that is notonly tailored for the manufacturing of solar cells, but forsemiconductor and other surface and near-surface modificationapplications as well. The development of this system is based on therelaxed specifications that solar cell fabrications require. It canprovide accurate doping and unique atomic profile tailoring capabilityfor solar cells (incorporating features from commonly-owned U.S. patentapplication Ser. No. 12/483,017, entitled “FORMATION OF SOLARCELL-SELECTIVE EMITTER USING IMPLANT AND ANNEAL METHOD,” filed Jun. 11,2009, and from commonly-owned U.S. Provisional Application No.61/131,698, entitled “FORMATION OF SOLAR CELL-SELECTIVE EMITTER USINGIMPLANT AND ANNEAL METHOD,” filed Jun. 11, 2008, which are both herebyincorporated by reference as if set forth herein). These include changein doping levels, resistance of contact, bus bar, fingers, contactresistance of metal-silicon interface, resistance of backsidemetallization, achieving the desired resistivity under the metal gridcontact (preferably 10 to 30 Ohms/Sq.) and in between the fingers(preferably greater than 100 Ohms/Sq.) to meet higher efficiency solarcells (incorporating features from commonly-owned U.S. patentapplication Ser. No. 12/482,980, entitled “SOLAR CELL FABRICATION USINGIMPLANTATION,” filed Jun. 11, 2009, commonly-owned U.S. ProvisionalApplication No. 61/131,687, entitled “SOLAR CELL FABRICATION USINGIMPLANTATION,” filed Jun. 11, 2008, commonly-owned U.S. patentapplication Ser. No. 12/482,685, entitled “SOLAR CELL FABRICATION WITHFACETING AND ION IMPLANTATION,” filed Jun. 11, 2009, and commonly-ownedU.S. Provisional Application No. 61/133,028, entitled “SOLAR CELLFABRICATION WITH FACETING AND ION IMPLANTATION,” filed Jun. 24, 2008,which are all hereby incorporated by reference as if set forth herein).It also meets the demands of future requirements for solar cell waferthickness, as well as contact metal width and spacing.

Moreover, the advantageous formation of selective emitter and BackSurface Field (BSF) and its ability to improve performance will bepossible (incorporating features from commonly-owned U.S. patentapplication Ser. No. 12/482,947, entitled “APPLICATION SPECIFIC IMPLANTSYSTEM AND METHOD FOR USE IN SOLAR CELL FABRICATIONS,” filed Jun. 11,2009, commonly-owned U.S. Provisional Application No. 61/131,688,entitled “APPLICATIONS SPECIFIC IMPLANT SYSTEM AND METHOD FOR USE INSOLAR CELL FABRICATIONS,” filed Jun. 11, 2008, commonly-owned U.S.Provisional Application Ser. No. 61/210,545, entitled “ADVANCED HIGHEFFICIENCY CRYSTALLINE SOLAR CELL FABRICATION METHOD,” filed Mar. 20,2009, and commonly-owned U.S. patent application Ser. No. 12/728,105,entitled “ADVANCED HIGH EFFICIENCY CRYSTALLINE SOLAR CELL FABRICATIONMETHOD,” filed Mar. 19, 2010). The present invention can be applied toas-grown single or mono-crystalline, poly or multi-crystalline orelectrical-grade or metallurgical-grade silicon, as well as very thinsilicon wafers and very thin film deposited silicon, or other materialsused for solar cell formation and other applications. The presentinvention can also be applied to multi junction devices, and can beextended to atomic species placement for any other material used infabrication of junctions and metal semiconductor interface enhancements.

FIG. 5 illustrates a cross-sectional side view of one embodiment of asolar cell 500 with a homogeneous implant in accordance with theprinciples of the present invention. Solar cell 500 comprises asemiconducting wafer with a p-doped region 510 and an n-doped region520. The n-doped region 520 is homogeneously doped to form a homogeneousemitter. An anti-reflective coating 560 is disposed over the n-dopedregion 520. The anti-reflective coating 560 preferably has a thicknessof between 70-80 nm. Metal contacts 550 are deposited onto the wafer,preferably having a width 554 of between 3-200 microns and being spacedapart by a width 552 of between 1-3 mm. A p-doped region 570 is formedin the wafer on the opposite side from the n-doped region 520, forming ahomogeneous BSF. A passivation layer 580 (e.g., Si₃N₄ or Al₂O₃) isdisposed over the bottom surface of the p-doped region 570, and a rearmetal contact layer 590 (e.g., Ag) is disposed over the bottom surfaceof the passivation layer 580.

FIG. 6 illustrates a cross-sectional side view solar cell 600, which issolar cell 500 with the addition of certain selective implants. Theseselective implants include n-doped selective emitter regions 630,selective metallic seed implants 655, and selective BSF regions 675.

In some embodiments, the present invention includes the use of ions ingas plasma that are accelerated to the substrate by the application ofpulses of negative potential to the substrate. The plasma istransitioned into a sheath at the proximity of the substrate, andapplications of a potential cause acceleration of ions resident in theplasma to be implanted. Such conformal doping of the substrate can beutilized to form homogenous doped regions, as well as selectively dopedregions through the use of a mask or other selective implantationtechniques. At the same time, the dopant profile can be tailored toprovide independent surface concentrations, shape of the profile, andthe junction depth, through pulse shape and plasma componentadjustments. Furthermore, through the use of the dopant stoichiometricratio and ratio of molecular radicals, the dopant profile can be furtherenhanced. Utilization of the pulse biasing of the substrate and possiblesubstrate back surface antenna or substrate movement can also providethe lateral positioning advantages required for selective implantations.

The present invention provides a system that can be independent of thesubstrate size, and as long as uniformity of plasma is conserved, thenmultiple pieces of substrate can be implanted simultaneously. Thisfeature allows productivities well in excess of 1000+ wph. Additionally,the present invention provides a non-line-of-sight implantation method,and thus, is able to dope areas that are constricted, such as thetextured surfaces of multi-grade silicon that may have hillocks andre-entrant features on the surface. Doping such surfaces is critical asabsence of doping may cause metal shunting.

One application of the present invention is to generate a homogeneousimplantation for emitter and Back Surface Field (BSF) doping. At thisstage, independent control of surface concentration, profile shape andjunction depth can play a significant role in meeting the lightconversion properties of a solar cell. Such implant capabilities willavoid the formation of a “dead layer” that is prevalent with incumbentdiffusion methods. These layers are formed as a result of un-activatedexcess near-surface dopants that are accumulated as diffusion is used toform the electrical junctions. Profile management achieved with thepresent invention's ion implantations can avoid such drawbacks.

FIG. 1 illustrates a cross-sectional side view of one embodiment of ahomogeneously doped solar cell 100 in accordance with the principles ofthe present invention. Solar cell 100 comprises a semi-conductingsubstrate 110, such as a silicon wafer. For the formation of the region120 where the cell 100 generates the electron-hole pairs, doping levelsof at least 100 Ohms/Sq. is preferred. In general, the excess of dopantsin this region 102 impede the generation and transport of such chargecarriers. This doping is typically a lower energy implant, such as lessthan 150 keV for boron, BF₂, phosphorous, arsenic, antimony, and othersimilar dopants. Such implants are carried out at a light concentration.In a preferred embodiment, the concentration of these implants is lessthan 1E15 cm⁻². The requirements for the uniformity of coverage forsolar cell applications are estimated to be between 5 to 10%. Similarhomogeneity is required in the plasma uniformity. It is envisaged thateach solar cell will be independently implanted, so as to attain thebenefits of the single wafer system. This feature provides significantcapability for implant, whereby tailoring the placement and activationof the dopant for selective emitter can prevent the formation of thetraditional dead layer issues.

FIGS. 2A-2C illustrate cross-sectional side views of different ways ofselectively implanting a solar cell 200 to form selective emitterregions 230 in accordance with the principles of the present invention.The solar cell 200 comprises a semi-conducting substrate 210, which hasbeen homogeneously doped to form a homogeneous emitter region 220,similar to homogeneous emitter region 120 in FIG. 1.

FIG. 2A illustrates a shadow mask method used to form selective emitterregions 230 in the semi-conducting substrate 210. In the shadow maskmethod, a physical mask 242 is used within the plasma implantertechnologies system to define the beam 240 to the exact dimensionrequired. The aspect ratio of the mask 242 is critical here, as it isestimated that typical energetic plasma ions can easily penetrate a 1:10aspect ratio, as has been demonstrated by lower energy plasma depositionmethods. The proximity of the mask 242 to the substrate 210 can beadjusted to use potential beam flare-out to the advantage ofconstruction of doped regions under the gridlines that are larger byapproximately +/−10 to 30 microns for a 100 micron wide gridline. Thisadjustment will allow for ease of subsequent gridline printing andalignment, and will provide an overlapping region for minimization ofany potential electrical leakage. In a preferred embodiment, thematerial used for the shadow mask 242 is innocuous to the processing,and is preferably conductive in order to not affect the implantationmethod. Sputtering of such material will determine the lifetime andusage of this mask 242, thus rendering it a consumable component with aregular replacement provision. The shape of the cutouts through whichthe ion beams 240 pass and surface conditions are also of criticalconsiderations to minimize contamination and sputtering rates. Typicalshaping that is already prevalent in the industry can be used for thefabrication of the shadow mask 242.

FIG. 2B illustrates a wafer mask method used to form selective emitterregions 230 in the semi-conducting substrate 210. Here, a mask 244 isplaced in contact with the semiconducting wafer 210. Such mask 244 canbe a hard or soft masking of the wafer prior to the implant step. Thewafer mask method can be achieved through the use of lithography,contact printing, or more prevalent screen printing steps. It can alsoutilize the already masked and opened processing steps used forformation of contact deposition. The distributed power density of thisimplantation method can lead to utilization of masking materials thatwere not used in the past implantation methods. An example of suchmaterials is the use of resist that is used, traditionally, in circuitboard fabrications and other low temperature masking materials.

FIG. 2C illustrates a localized plasma beam shaping method to formselective emitter regions 230 in the semi-conducting substrate 210.Here, the required pulsing of the beam and an envisaged back surfaceantenna can be made into a closed loop control so that plasma isdirected selectively into certain regions of the substrate. In someembodiments, additional grid structures, such as those discussed infurther detail below, could be used to further optimize the shape of theplasma beam, whereby a voltage can be applied, both negative and/orpositive, to achieve such shaping. As seen in FIG. 2C, the selectedregions 230 are in alignment with the locations where a voltage 246 isdirectly applied to the back surface of the semiconducting wafer 210.This method may be more applicable for thinner wafers. Alternatively, acombination of the pulsing of the plasma and possible positioning of thesubstrate can be used to generate areas of high and low doping.Overlapping of these regions can provide an optimized controlled flow ofelectron holes from the low-doped regions, suited for light conversion,to the highly-doped selectively implanted regions, suited for electricalcontact gridlines. One could envisage regions of high and low dopingoverlaps as the substrate, under precise controlled motions, movesbeneath the ion beams. The different regions will not have distinctiveboundaries, and a gradual change of doping levels can provide anadvantage in flow of charges within the substrate. Such variability inthe lateral doping can enhance the operation of the cells.

FIG. 3 illustrates a cross-sectional side view of one embodiment of asolar cell 300 with contact gridlines 350 in accordance with theprinciples of the present invention. The solar cell 300 comprises awafer. In some embodiments, the wafer 110 is a 156×156 mm wafer.Preferably, the wafer is formed of a semiconductor material, such assilicon (single or multi-crystalline), and comprises a p-n junction. Thep-n junction is formed from a p-type doped region 310 and an n-typedoped region 320 being disposed next to one another. Metal contact lines350 are printed, or otherwise formed, on the surface of the wafer. It iscontemplated that the contact lines 350 can also be formed fromconductive material other than metal. In some embodiments, conductivefingers (not shown) are also disposed on the surface of the wafer tocollect the electrical charge from the contact lines and carry it out toan external load.

In operation, as light comes into the semiconductor material of thewafer through the exposed surface between the contact lines 350, it isconverted into electron-hole pairs, typically within the n-type dopedregion 320. The electrons go one way, getting attracted into thecontacts 350, while the holes go the other way, towards the p-type dopedregion 310. The more dopant there is within a particular region, themore the electron-hole pairs are recaptured within that region,resulting in more lost electricity. Therefore, it is beneficial tocontrol the level of doping for different regions. In regions where thelight is to be converted into electron-hole pairs, the level of dopingshould be relatively low. In regions where the charge is to go throughthe contact lines 350, the level of doping should be high. Regions 320represent a homogeneous emitter region that has been homogeneously dopedwith a low level of n-type dopant. Regions 330 disposed beneath thecontact lines 350 near the surface of the wafer represent selectiveemitter regions that have been selectively doped with a relatively highlevel of n-type dopant.

As a result of minimizing the dopant concentration (thereby, maximizingthe resistivity) of the homogeneous emitter region and maximizing thedopant concentration (thereby, minimizing the resistivity) of theselective emitter regions, the ability of the solar cell to transfer thegenerated electrons from the homogeneous emitter region through theselective emitter regions to the contact lines is increased, while therisk of losing electricity to electron-hole pair recombination isreduced. Additionally, although bigger contact lines can conduct moreelectricity, they also block more light from entering the solar cell andbeing converted into electrons. By maximizing the dopant concentrationof the selective emitter regions near the contact lines, the contactlines can actually be made thinner, thereby allowing more light to enterthe solar cell, while improving the solar cells ability to transfer theelectrons from the electron-hole pair generating region to the contactlines.

In some embodiments, the homogeneously doped region is doped to have asheet resistance in a range of approximately 80 Ohms/square toapproximately 160 Ohms/square, while the selectively doped regions aredoped to have a sheet resistance in a range of approximately 10Ohms/square to approximately 40 Ohms/square. In some embodiments, thehomogeneously doped region is doped to have a sheet resistance ofapproximately 100 Ohms/square or greater, while the selectively dopedregions are doped to have a sheet resistance of approximately 25Ohms/square or less.

In some embodiments, the selectively doped regions 330 are laterallyspaced apart from one another a distance in the range of approximately 1mm to approximately 3 mm. However, it is contemplated that other spacingdimensions are within the scope of the present invention. Additionally,for selective emitter applications, the solar cell industry is expectedto require the implanted contact gridlines 350 to have a width from 200microns down to less than 50 microns.

Plasma implantation systems can be used for the formation and adjustmentof the work function and the band gap engineering for the contactdeposition, through the formation of near-surface metal-silicide.Through a very light dose implantation of a metallic species (such asTa, Ti, etc.) at locations near the surface of the wafer, ametal/silicon contact is improved markedly. Such seed implants or workfunction adjustment implants can improve contact performance.

FIG. 4 illustrates one embodiment of a plasma immersion implantationsystem 400 in accordance with the principles of the present invention.This system is disclosed in U.S. Provisional Application Ser. No.61/185,596, filed Jun. 10, 2009, entitled “APPLICATION SPECIFIC PLASMAIMPLANT SYSTEM FOR USE IN SOLAR CELL FABRICATIONS,” which is herebyincorporated by reference in its entirety as if set forth herein. Thesystem 400 comprises a vacuum chamber 410, a gas input system 420, aplasma generator 430, one or more vacuum pumps 450, and a high-voltagepulser 480. The gas input system 420, the plasma generator 430, and thevacuum pumps 450 work together to provide plasma 460 within the vacuumchamber 460 at a location near a target substrate 440. The high-voltagepulser 480 is used to negatively bias the target substrate 440. Examplesof pulsers that can be used include hard-tubed pulsers, such as planartriode, power tetrode, and hobertron. It is contemplated that otherpulsers can be used as well. As a result of the high negative voltagepulse being applied to the target substrate 440, a sheath between theplasma 460 and the target substrate 440 forms, and ions 470 from theplasma 460 are accelerated into the target substrate 440. This plasmaimmersion implantation technique removes the need for any mass analysis.It provides acceptable power density and excellent productivity.

This implantation system has unique capabilities for solar cellapplications. In order to meet the productivity demand of the solar cellindustry, multiple-piece simultaneous implantation is envisaged. For atypical four-piece substrate of 156×156 mm pseudo-square, with a totalarea of 0.25 m², such a system will preferably comprises a large plasma,with a height of 0.3 m and a sheath of 0.5 cm, and a total chamberheight of 1 m, with generation of plasma peak currents up to 15 A. Thesystem is useful in meeting the pulse energy demands of the solar field,which are variable and preferably less than 150 kV. These supplies willbe plug compatible and, depending on the species and mass used, willprovide the required depth of penetration.

In some embodiments, the system is used for single species implantation,so as to avoid any cross contamination of dopants. Additionally, in someembodiments, the internal portion of the chamber 410 is clad withappropriate material so as to minimize the potential of metallic andother unwanted contamination.

Preferably, components such as the vacuum chamber, multiple-pass loadlock, gas delivery system, and automation and factory interfaces areconfigured in-line with such an application specific system or in-linewith a typical high volume solar cell manufacturing system. In preferredembodiments, the system operates with a productivity of 1000+ wafers perhour to match the automation of the solar cell fabrication lines.

The dopant profile can be modified through the pulse shape adjustment tomeet the tailoring required by solar cell PV fabrications. One method isto use a passivation pulse-forming network mechanism. The profile canfurther be tailored by the use of plasma content adjustment, which canbe achieved through the special use of micro-wave or RF coupling, or anymultiple of prevalent plasma formation technology, with plasma so as tomodify the plasma conditions and thus control the break up of theconstituents, which can affect the stoichiometric ratio of the dopantand the molecular ratio of radicals present in the plasma. For example,for the use of solid phosphorous, its various components (such as P⁻,P⁺⁺, P⁺⁺⁺, P₂ ⁺, P₃ ⁺, P₅ ⁺, etc.) can be used to ensure that nearsurface tailoring is achieved. Such tailoring can also be used for otherdopants, such as p-type Boron.

A direct side benefit of plasma implant technology is the prevalence ofhydrogen (e.g., if the source of the dopant is PH₃ or B₂H₆). Thehydrogen will be implanted simultaneously and at higher energies,helping to provide an auto-gettering effect that is unique and demandedfor poorer quality solar cell materials.

Variability of the energy during the pulsing of the plasma, where it canbe distinct or as a continuum, can also be employed to form the requiredprofile and manage independent surface concentration, atomic profileshaping and junction depths. This could be distinct and in known stepsor can be as continuum to appropriate pauses at required energy tocontrast the desired profiles.

The average distributed power density of this system lends itself toimplantation of very thin wafers (i.e., less than 20 microns) andensures that thicker wafers remain at a temperature of less than 100° C.throughout the process. Such distributed power density allowsutilization of various hard masking (e.g., resist) materials that maynot have been considered before with diffusion, which employs hightemperature, and directed implant, which employs high average powerdensity. Depending on the desired PV applications, the averagedistributed power density of the present invention can be modulated byadjusting the frequency and duration of pulses for high (greater than300° C.) and low (less than 100° C.) substrate temperature.

No subsequent diffusion is required. Lower temperature anneal as low as500° C. can provide enough activation and damage anneal for fabricationof a PV cell. Plasma implantation, due to its high productivity, canprovide higher doses, and thus, if only a portion of the dopant isactivated, then the desired resistivity and performance can be achieved.

In some embodiments, various materials or compounds are used to providesurface passivation in solar cell fabrication. For example, in someembodiments, Si₃N₄ or SiO₂ is deposited and/or grown at elevatedtemperatures or using pyrogenic growth methods. Such methods are limitedto prevalent chemistry and molecular make up cannot be changed. However,through the use of the plasma implant technology of the presentinvention, the molecular make-up can be adjusted for improvements ofpassivation properties. Formation of SiN_(x) or introduction of excessnitrogen can provide improvement of passivation properties of this film.

Despite the advantages of the plasma immersion implantation systemdiscussed above, the present invention provides an even more beneficialimplantation system in the form of a plasma grid implantation system.The plasma grid implantation system provides the beneficial powerdensity of beamline implantation, while also providing the productivityof plasma immersion technology.

FIG. 7 illustrates a cross-sectional side view of one embodiment of aplasma grid implant system 700 in accordance with the principles of thepresent invention. System 700 comprises a chamber 710 that houses afirst grid plate 750, a second grid plate 755, and a third grid plate757. The grid plates can be formed from a variety of differentmaterials, including, but not limited to, graphite, silicon carbide, andtungsten. Each grid plate comprises a plurality of apertures configuredto allow ions to pass therethrough. A plasma source provides a plasma toa plasma region of the chamber 710. In FIG. 7, this plasma region islocated above the first grid plate 750. In some embodiments, the chamberwalls are configured to repel ions in the plasma region using anelectric field. For example, in some embodiments, one or more magnets790 are coupled to the wall of the chamber 710. The electric field isused to push the plasma off the walls, thereby maintaining a gap betweenthe plasma and the chamber walls, and avoiding any sputtering off of thewall material into the plasma. A target substrate is positioned on theopposite side of the grid plates. In FIG. 7, the target substrate islocated below the third grid plate 757. As will be discussed in furtherdetail below, the target substrate is preferably supported by anadjustable substrate holder, thereby allowing the target substrate to beadjusted between a homogeneous implant position 740 a and a selectiveimplant position 740 b.

The main feature of this system 700 is the use of plasma ions that areaccelerated towards the target substrate by application of a DC orpulsed potential to the first grid plate 750. These ions are implantedinto the substrate. The deleterious effect of secondary electronsresulting from the impingement of ions on the substrate and othermaterials is avoided through the use of the second grid plate 755, whichis negatively-biased with respect to the first grid plate 750. Thisnegatively-biased second grid plate 755 suppresses the electrons thatcome off of the substrate. In some embodiments, the first grid plate 750is biased to 80 kV and the second grid plate 755 is biased to −2 kV.However, it is contemplated that other biasing voltages can be employed.The third grid plate 757 acts as a beam defining grid and is preferablygrouned. It is positioned in contact with or very close to the surfaceof the substrate in order to provide a final definition of the implant.This grid plate 757 can act as a beam defining mask and provide thecritical alignment required, if a selective implant is required. Thethird grid plate 757 can be configured in accordance with the shadowmask embodiment of FIG. 2A or the wafer mask embodiment of FIG. 2B inorder to achieve beam-defining selective implantation. Additionally, Thethird grid plate 757 can be replaced or supplemented with any form ofbeam shaping that does not require a mask, such as the pulsed beamshaping embodiment of FIG. 2C.

It is contemplated that the grid plates can be spaced apart in a varietyof ways. In one embodiment, the first grid plate 750 is separated fromthe second grid plate 755 by a distance of approximately 12 mm, and thesecond grid plate 755 is separated from the third grid plate by adistance of approximately 3 mm. However, other measurements can beemployed.

In general, several grid arrangements, such as triode, tetrode andothers, can be envisaged, where the grid arrangements are used tooptically control the ion beam-lets. For the case of homogenousimplantation, the defining mask can be removed to provide homogenouscoverage of the wafer. The position of the wafer for selectiveimplantation, with shadow mask, and for homogenous implantation can bealtered to benefit from the multiple grids beam definition. For example,for the selective implantation, the wafer 740 b is moved close to themultiple grid plate assembly (750, 755, 757), whereas, for thehomogenous implantation, the wafer 740 a is moved far enough from thegrid plate assembly (750, 755, 757) to provide a uniform beam, which isformed as a result of space charge expansion of the beam-lets 776. Thisgrid plate assembly can be used to further focus the beam-lets 776 intoknown shapes onto the substrate, such as by adjusting the position ofthe plates with respect to one another, thereby eliminating the need forany shadow masking or any other substrate masks. This grid plateassembly arrangement enables the use of DC or pulsed bias for theacceleration of ions and minimizes the back streaming electrons that hashampered plasma immersion technology by limiting the energy range andmaking the pulser/PSU cost prohibitive. This dramatically simplifies thepower supply needed.

Additionally, by decoupling the plasma formation from the ionacceleration, the present invention allows for independent methods to beused for the formation of the plasma above the grid plates. The gridplates can provide some degree of beam definition. For example, theextracted ion beam can be focused to a particular dimension of selectiveemitter applications.

In plasma grid implant system 700, the chamber 710 is configured toallow the plasma to form and expand. As previously discussed, the firstgrid plate 750 is at a positive potential with respect to ground. Byshaping this biased grid plate (electrode) and managing the shape of themeniscus 780 formed above each of its openings, ions are extracted andoptically shaped.

As previously discussed, the second grid plate 755, which is negativelybiased, suppresses the back streaming electrons. The substrate and thethird grid plate 757 (whether it is configured as a shadow mask or awafer mask) can be placed at a very close proximity to the second gridplate 755 to utilize the pattern definition by the grid assembly, asshown with the position of substrate 740 b. At this position, the ionsextracted are in the shape of beam-lets that are well defined andimplanted in selective regions in the substrate 740 b. The substrate canalso be positioned further away from the first and second grid plates750 and 755 to achieve a homogenous and uniform implant either with orwithout the use of a shadow mask, such as with substrate 740 a. As seenwith the positioning of substrate 740 a, the beam-lets 776 have mergeddue to space charge expansion. Alternatively, one position could be usedfor both homogeneous and selective implantation, where the selectiveimplant is performed in the presence of a shadow mask or a wafer mask inorder to provide the selectivity required.

A beam of ions exiting past an aperture is divergent by its nature,which is because the typical equilibrium of plasma is convex. The ionsrepel each other because of their like electric charge and they haverandomly orientated velocities due to thermal motion within the plasma.Therefore, careful design of the grid plate apertures and the plasmacondition is necessary to control both the emittance of ions and systemacceptance to the ion beam. The emittance is a measure of the beamquality. Typically, high quality beams have low emittance, which meansminimal loss of ions during transmission. This has to be balancedagainst the system specific phase-space boundary such that the beam fitswithin this boundary or has good acceptance.

The control of ion divergence in the system of the present invention isachieved primarily through adjusting the shape of the ensuing meniscus780 at the plasma boundary as it enters the first grid plate electrode750. Such shaping can be controlled by adjusting the voltage differencebetween various electrodes, the shapes of the opening and spacingbetween various electrodes, the temperature of the plasma, how muchplasma gas is used, the density of the plasma and the ion species andcurrent being extracted. For the concave dome shape of meniscus 780 inFIG. 7, the second grid plate 755 has to have a negative potential withrespect to the first grid plate 750, and the plasma ion density has tobe less than the plasma boundary. Although FIG. 7 shows meniscus 780having the shape of a dome, it is contemplated that the meniscus 780 canbe managed in the form of other shapes as well, including, but notlimited to, a complete inversion of the dome shape. The shape of themeniscus 780 can be used to shape the resulting ion implantation beam.Whereas a dome-shaped meniscus, such as meniscus 780 shown in FIG. 7,will typically result in a narrowed beam, an inverted dome-shapedmeniscus will typically result in an expanding beam.

FIG. 8 illustrates a cross-sectional 3-dimensional perspective view ofanother embodiment of a plasma grid implant system 800, similar tosystem 700, in accordance with the principles of the present invention.System 800 comprises a chamber 810 that houses a first grid plate 850, asecond grid plate 855, and a third grid plate 857. The grid plates canbe formed from a variety of different materials, including, but notlimited to, silicon, graphite, silicon carbide, and tungsten. Each gridplate comprises a plurality of apertures configured to allow ions topass therethrough. A plasma source provides a plasma to a plasma regionof the chamber 810. In FIG. 8, this plasma region is located above thefirst grid plate 850. In some embodiments, a plasma gas is fed into theplasma region through a gas inlet 820. In some embodiments, a vacuum isapplied to the interior of the chamber 810 through a vacuum port 830. Insome embodiments, an insulator 895 is disposed around the exterior wallof the chamber 810. In some embodiments, the chamber walls areconfigured to repel ions in the plasma region using an electric field,as discussed above.

A target wafer 840 is positioned on the opposite side of the grid platesfrom the plasma region. In FIG. 8, the target wafer 840 is located belowthe third grid plate 857. As previously discussed, in some embodiments,the target wafer 840 is supported by an adjustable substrate holder,thereby allowing the target wafer 840 to be adjusted between ahomogeneous implant position (closer to the grid plates) and a selectiveimplant position (farther away from the grid plates). Plasma ions areaccelerated towards the target wafer 840 by application of a DC orpulsed potential to the first grid plate 850 in the form of ion beams870. These ions are implanted into the wafer 840. The deleterious effectof secondary electrons resulting from the impingement of ions on thewafer 840 and other materials is avoided through the use of the secondgrid plate 855, which is negatively-biased with respect to the initialgrid. This negatively-biased second grid plate 855 suppresses theelectrons that come off of the wafer 840. In some embodiments, the firstgrid plate 850 is biased to 80 kV and the second grid plate 855 isbiased to −2 kV. However, it is contemplated that other biasing voltagescan be employed. The third grid plate 857 acts as a beam defining gridand is preferably grounded. It is positioned in contact with or veryclose to the surface of the substrate in order to provide a finaldefinition of the implant. This grid plate 857 can act as a beamdefining mask and provide the critical alignment required, if aselective implant is required. The third grid plate 857 can beconfigured in accordance with the shadow mask embodiment of FIG. 2A orthe wafer mask embodiment of FIG. 2B in order to achieve beam-definingselective implantation. Additionally, The third grid plate 857 can bereplaced or supplemented with any form of beam shaping that does notrequire a mask, such as the pulsed beam shaping embodiment of FIG. 2C.

It is contemplated that the apertures in the grid plates can beconfigured in a variety of different ways. FIGS. 9A-9B illustratecross-sectional side views of different grid plate apertures throughwhich the ion beams pass. In FIG. 9A, grid plate 950 a comprises anaperture 965 a that has a uniform width. When the grid plate 950 a ispositively-biased, an electric field is formed around it. This electricfield is illustrated by electric field lines 951 a and 953 a, whichfollow the contour of the grid plate 950 a. As an ion beam passesthrough the aperture 965 a, field lines 951 a and 953 a define the pathalong which the ions travel. As a result, the electric field chokes theions as they pass through the aperture 965 a, thereby narrowing thewidth of the resulting ion beam. In FIG. 9B, grid plate 950 b comprisesan aperture 965 b that has a width that expands from top to bottom.Similar to grid plate 950 a in FIG. 9A, when the grid plate 950 b ispositively-biased, an electric field is formed around it. This electricfield is illustrated by electric field lines 951 b and 953 b, whichfollow the contour of the grid plate 950 b. As an ion beam passesthrough the aperture 965 b, field lines 951 b and 953 b define the pathalong which the ions travel. Since the width of the opening 965 bexpands as from the point where the ions enter the aperture 965 b to thepoint where the ions exit the aperture 965 b, this apertureconfiguration provides a resulting ion beam that can cover a largersurface area than the uniform configuration.

FIG. 10 illustrates a cross-sectional side view of one embodiment ofplasma ions passing through grid plates in accordance with theprinciples of the present invention. Similar to FIGS. 7-8, a plasma 1060is provided above first and second grid plates 1050 and 155, which arepositively and negatively biased, respectively, as previously discussed.A meniscus 1080 is formed at the plasma boundary as the plasma ionsenter aperture of the first grid plate electrode 1050. The ion beam 1070passes through the first grid plate electrode 1050 and then through thesecond grid plate electrode 1055 before implanting a target substratedisposed below the grid plate assembly. The top and bottom surfaces ofthe grid plates can be configured to manage the ion beam 1070 in avariety of ways. For example, in some embodiments, the bottom surface1052 of the first grid plate 105 can be angled inward in a femaleconfiguration and the top surface 1054 of the second grid plate 1055 canbe angled outward in a male configuration so that the entrance to theaperture in the second grid plate 1055 can be brought closer to the exitof the aperture in the first grid plate 1050.

FIGS. 11A-11B illustrate plan views of different grid plate apertures inaccordance with the principles of the present invention. FIG. 11A showsgrid plate 1050 a having a plurality of apertures 1165 a formedtherethrough. These apertures 1165 a are substantially circular. FIG.11B shows grid plate 1050 b having a plurality of apertures 1165 bformed therethrough. These apertures 1165 b are substantially elongatedand rectangular slots. In some embodiments, the elongated slots 1165 bhave dimensions of a few 100's of microns wide by 10's of centimeterslong at a spacing of 1-2 mm in order to maximize the utilization of theplasma beam-lets and create the image of the final beam-defining grid.However, larger spacing could be envisaged, whereby the space chargebeam expansion is employed to get a uniform beam to provide the coverageneeded. It is contemplated that the apertures can be formed in othershapes besides circular and rectangular. The shape and the dimensions ofthe openings in the grid plates depend on the shape and dimension of theseries of beam-lets required for the particular implantation. Beamoptics calculations and considerations, such as emittance and spacecharge effects, define the shape of such openings and the materialsutilized for the fabrication. The opening in the first grid plate isparticularly critical in order to maintain the shape of the resultingmeniscus of plasma at the grid plate openings. The shape of thismeniscus is critical for the subsequent optical properties of the ionbeam. The position, shape, and applied negative potential field at thesecond grid plate and its possibility of interference in the shape ofthe meniscus is critical to ensure passage of the ion beam with minimumion optical effect, while still being sufficient to inhibit flow ofelectrons in the reverse direction.

The combination of the two, three or more grid plates simplifies the DCor plused power supply units for energizing the grid plates. For theseapplications, an accelerating potential of less than 150 kV isenvisaged, with a negatively biased grid plate of approximately −5 kV.The grid plate spacing between the first grid plate and the second gridplate in a reasonable vacuum is preferably in the order of a fewcentimeters, while the spacing between the second grid plate and thethird grid plate is preferably in the order of a few millimeters.Certain calculations and distances in vacuum can be used for the appliedvoltage.

The second grid plate electrode can also be connected to a pulse formingnetwork to optimize the extracted ion qualities, such as increaseddensity of desired ion species and ion energy, in order to optimize theimplanted junction profile. The plasma source in the chamber can also bepulsed-biased using the similar pulse-forming network in modulation withthat of the second grid plate electrode in order to optimize theextracted ion qualities as mentioned in above.

The system of the present invention provides a simplified arrangementthat lends itself well into formation of implant chambers, as opposed tosingle beam (including widened beams) and scanning mechanisms that havemade ion implantation systems into complex multi-module systems. Suchsimple ion beam generation (via plasma) and ion acceleration (via gridplate assembly) can be constructed into a single chamber assembly thatcan be combined with a general wafer handling platform. Such a platformcan support other processes in the fabrication lines, such as vacuumdeposition, etching and metallization. FIG. 12 illustrates a plan viewof one embodiment of a load-locked implantation system 1200 inaccordance with the principles of the present invention. The targetwafer can be loaded into a vacuum chamber 1210, where a robot can thentransfer the wafer to one of several load-locked chambers under vacuum.For example, the wafer can be moved into one of several implantationsystems 1220, such as system 700. The wafer can also be moved into anitridization chamber 1230 or an oxidation and anneal chamber 1240, suchas an RTP anneal chamber.

Furthermore, such a platform can support a multi-stage vacuum pumpingscheme that denies the need for specific load-locking mechanisms. FIG.13 illustrates a cross-sectional view of one embodiment of a multi-stagedifferentially pumped implantation system 1300 in accordance with theprinciples of the present invention. In the system, the target wafer1380 is moved through multiple stages before and after reaching theimplantation stage. In some embodiments, the wafer 1380 is moved via aconveyor belt 1390. However, it is contemplated that other transfermeans can be employed. In FIG. 13, the wafer 1380 moves from right toleft, going through stage 1310, then stage 1320, and then stage 1330,before reaching stage 1340, with each stage applying a stronger vacuum.Stage 1310 applies a small vacuum V1 (e.g., resulting in a pressure of0.1 millibars). Stage 1320 applies a larger vacuum V2 than stage 1310(e.g., resulting in a pressure of 0.01 millibars). Stage 1330 applies aneven larger vacuum V3 than stage 1320 (e.g., resulting in a pressure of10⁻⁴ millibars). Finally, Stage 1340 applies the largest vacuum V4. Atstage 1340, the plasma grid implantation system discussed above is used,employing the multiple grid plate assembly (e.g., grid plates 1342 and1344). Once the implantation stage is completed, the wafer 1380 movesthrough stage 1350, then stage 1360, and finally stage 1370, each stageapplying a smaller vacuum than the last stage.

The vacuum chamber, multiple pass load lock or multi-stageddifferentially-pumped pass-through, gas delivery system and automationand factory interfaces can also be configured in-line with anapplication specific implantation system or configure in-line with atypical high volume solar cell manufacturing system. Preferably, theproductivity of the system is 1000+ wafers per hour to match theautomation of the solar cell fabrication lines.

For homogenous implantation for emitter and back surface field (BSF)doping, independent control of surface concentration, profile shape andjunction depth can play a significant role in meeting the lightconversion properties of a solar cell. Such implant capabilities willavoid the formation of “dead layer” for emitter, which is prevalent withincumbent diffusion methods. These layers are formed as a result ofun-activated excess near surface dopants accumulated as diffusion isused to form the electrical junctions. Profile management achieved withion implantation can avoid such drawbacks. The BSF implant can be usedto displace the present method of aluminum metallization that isencumbered with a series of mismatch issues. The control for such BSFimplantation will also provide key advantages in the formation of backcontact.

For the formation of the regions where cells generate the electron holepairs, doping levels of at least 100 Ohms/Sq. is preferably used. Ingeneral, the excess of dopants in this region impedes the generation andtransport of such charge carriers. This region is typically a lowerenergy implant, such as less than 150 keV for boron, BF2, phosphorous,arsenic, antimony, and other similar n or p-type dopants. Such implantsare carried out at a dose of less than 1E16cm⁻². The requirements forthe uniformity of coverage for solar cell applications are estimated tobe between 5 to 10%. This requires similar homogeneity in the plasmauniformity. It is envisaged that each solar cell will be independentlyimplanted, so as to attain the benefits of the single wafer system,which is a significant capability for implantation, whereby tailoringthe placement and activation of the dopant for the selective emitterregions can avoid the formation of the traditional dead layer issues. Asimplantation is a single sided process, there will be no necessity forthe edge etch or cutting of the solar cells.

This capability is achieved by positioning the target substrateunderneath the grid assembly electrodes only at a distance far enoughwhere the beam-lets have converged due to space charge expansion to auniform beam. This positioning can be achieved through the use of anelevator that moves the target substrate to and away from the gridassembly. The plasma intensity variation and variation of the potentialon the second grid plate and, at times, on the first grid plate alsoprovide the uniformity of less than 5% (one sigma) in the beam.

As mentioned above, another application of the present invention is touse some form of masking to generate selectively implanted regions. Suchregions can be n or p-type depending on whether it is for a selectiveemitter or a selective BSF. It can also be a series of interdigitatedalternate doping (n/p/n/p . . . etc) regions for all back contact solarcells. For this application, the target substrate plus the mask could beheld very close to the grid assembly, where the beam-lets are much moredistinct and spaced apart. Alternatively, one could rely on the shadowmask at the wafer to provide the implant selectivity required. Thedimensions of the grid plate openings can match the substrate mask forbest utilization of the ion beam. Although, this is not critical aspresence of the mask on the wafer will ensure selectivity.

In another embodiment, the plasma grid implant system of the presentinvention is used for the formation and adjustment of the work functionand the band gap engineering for the metal/semiconductor contactregions. In this step, through metallic species implantation atlocations very near the surface, metal/silicon contact is improvedmarkedly. A similar system, as discussed above, can be used to do thegrid line implants after the selective doping implants. Such seedimplants or work-function-adjust implants can improve contactperformance.

The control of the dopant atomic profile can also be made through theprevalence of multiple species available in a plasma. Each plasmacondition will have a mix of charged species at varying fractions. Suchfractions can be controlled and are repeatable. Such mixed species is ofthe desired atoms at molecular and multiple charge state and, for thesame applied voltage bias, will have varying energies. For example, asingle type of dopant material can be provided to a plasma generator,where it is broken up into a plurality of dopant species. The targetsubstrate is then implanted with the plurality of dopant species. Forexample, using a plasma gas such as phosphine, can provide differenttypes of implants with only one implantation step because of thedifferent charges and different masses of the resulting dopant species(P⁺, P⁺⁺, P⁺⁺⁺, P₂ ⁺, P₃ ⁺, P₅ ⁺, formed from the phosphine being brokenup. The amount of each dopant species (i.e., its percentage relative tothe total ion beam) can be adjusted by adjusting the conditions of theplasma, such as the power used. In this respect, a user can manage thebreak-up of the dopant and can tailor it as desired (e.g., 80% P⁺, 10%P⁺⁺, 5% P⁺⁺⁺, 3% P₂ ⁺, etc.). Each species is implanted depth becausetheir energies are different. This feature can be used for formation ofmultiple atomic profiles that net into the desired shape ideal for thefabrication.

The use of the grid plates of the present invention with limitedopenings between the chamber region that contains the plasma and thechamber region that contains the substrate ensures effectivedifferentially-pumped regions. In the plasma region, vacuum has to becontrolled in order to allow for the formation of the plasma andminimize any other unwanted species presence. However, adifferentially-pumped substrate chamber is also critical because thevacuum can be somewhat variable due to the impact of the substratesurface out-gassing and the load-locking burst of gas. This gridassembly also provides protection against free radicals and otherpotential airborne hydrocarbons that can affect the surface of thesubstrate adversely.

The formation of the beam-lets and their subsequent expansion, as aresult of natural space charge beam expansion, can be utilized toprovide lateral selective region implantation or homogenousimplantation. As previously discussed, for the selective implant, thetarget substrate and a defining grid or a shadow mask can be positionedvery close to the third grid plate or in a similar position as for thehomogenous implant. The minimum distance for the substrate's proximityto the grid is determined by the voltage holding and applied potentialto the grid assembly. The role of the beam-defining shadow mask is toensure fidelity in the positioning of the implanted region. This maskcan be used for improving the alignment of the mask to the substrate,and thus, ensures a higher degree of overlap between selective implantedregions and the subsequent metal grid lines that are screen or jet inkprinted on the solar cell.

Such conformal doping of substrate can be utilized to form bothhomogenous and selective emitter regions through use of a mask and otherunique selective doping techniques. At the same time, the dopant profilecan be tailored to provide independent surface concentration, shape ofthe profile and the junction depth, through DC voltage, exposure time,and substrate motion underneath the beam and plasma componentsadjustments. Further more, by the use of the dopant stoichiometric ratioand ratio of molecular radicals present in the plasma, the dopantprofile can be further enhanced. This method does not preclude theutilization of the pulsing of the substrate and possible substrate backsurface antenna or substrate movement to provide the lateral positioningadvantages required for selective implantations.

The system of the present invention can be configured independently ofthe substrate size. Furthermore, as long as uniformity of plasma isconserved, multiple pieces of substrate can be implanted simultaneously,thereby allowing productivity well in excess of 1000+ wph.

Additionally, the present invention can provide a non-line-of-sightimplantation method, and thus, is able to dope areas that areconstricted, such as the textured surfaces of multi-grade metallurgicalsilicon that may have hillocks and re-entrant features on the surface.Doping such areas is critical, as absence of doping may cause metalshunting. Pulsing of the target substrate can be employed to direct theions these constricted areas.

The implantation system of the present invention provides uniquecapabilities for solar cell applications. In order to meet theproductivity demand of the solar cell industry, multiple-piecesimultaneous homogenous implantation can be employed, followed by amasked and selective implantation. However, such implantations can be inany order. For a typical four piece substrate of 156×156 mmpseudo-square, with a total area of 0.25 m², such a system preferablycomprises a chamber with a dimension of 0.4 m in height by 1.2 m inwidth. This allows for plasma and grid overflow regions to ensureuniformity of implantation on the substrate. Such a system can be usedin conjunction with a multi-stage differentially-pumped non-load lockedarrangement, as previously discussed, whereby the substrate can betransported on a conveyor or other transport mechanism from anatmospheric side to a vacuum side, and visa versa, which simplifies thewhole system and reduces the material cost.

The system of the present invention is expected to generate average ioncurrent density of at least 0.5 mA/cm² at 90 kV of high voltage bias,which is derived from the following equation:

$I_{p} = {\frac{{D \cdot {{Ze}\left( {1 + \gamma_{SE}} \right)}}A}{f\; \Delta \; {t \cdot T}} \times a \times b}$

where, assuming a typical plasma system:

-   -   D=dose [cm-2]    -   f=pulse frequency [s]    -   Δt=pulse duration [μs]    -   I_(p)=peak current [A]    -   T=implantation time [s]    -   Z=charge state    -   e=electron charge [A-s]    -   γSE=secondary electron emission coeff.    -   A=surface area [cm⁻²]    -   a=stoichiometric ratio of dopant    -   b=molecular ratio of radical in plasma        One example provides a gas of PH₃, a dose of E16 cm⁻², a        stoichiometric ratio of dopant of 0.25, and a molecular ratio of        radical in plasma of 0.3.

The system of the present invention can be used for multiple species, soas to avoid any cross contamination of dopants. Additionally, in someembodiments, the internal walls of the chamber is clad with appropriatematerial so as to minimize the potential of metallic contamination, andother unwanted contamination, and ease of cleaning, servicing andreplacement. Furthermore, as previously discussed, a confining field,such as an electric field, can be added to the internal chamber walls inorder to limit the interactions of the plasma or the ions from thesurrounding materials. In some embodiments, the ion beam can be skewedand a unique field can be applied so as to only allow the passage of therequired species to the target substrate.

The profile of the solar cell can further be tailored by the presentinvention's use of plasma content adjustment, which can be achievedthrough the special use of micro-wave or RF coupling with plasma so asto modify the plasma intensity and temperature, and thus control thebreak-up of the constituents, as previously discussed. This adjustmentcan affect stoichiometric ratio of dopant and the molecular ratio ofradicals present in the plasma. For example, for the use of solidphosphorus, its various components such as P⁻, P⁺⁺, P⁺⁺⁺, P₂ ⁺, P₃ ⁺, P₅⁺, etc. can be used to ensure that near surface tailoring is achieved.This adjustment can be used for other dopants as well, such as n-typeboron.

Another benefit of the plasma implant technology of the presentinvention is the prevalence of hydrogen, if an appropriate source of thedopant is used, such as PH₃ or B₂H₆. The hydrogen will simultaneouslyimplanted with the other dopant, and at higher energies, which will helpprovide auto-gettering and surface passivation effects that are uniqueand useful for poorer quality solar cell materials.

A variable energy accelerating the plasma, either in distinct steps oras a continuum, can also be employed to form the required profile andmanage to generate an independent surface concentration, atomic profileshaping and junction depths. This could be distinct and in known steps,or can be as continuum to appropriate pauses at required energy tocontrast the desired profiles.

The average distributed power density provided by the present inventionlends itself to implantation of very thin wafers (e.g., less than 20microns) whether they are independent or mounted on other substrates,and ensures that thicker wafers remain at a temperature of less than100° C. throughout the process. The distributed power density alsoenables the processing of non-silicon-based substrates such as CdTe,CIGS, and a-Si thin-film substrate, which require low substratetemperature operation. Wafer cooling and heating may be necessary, inparticular as the wafer thickness is reduced, which can be provided inthe form of typical backside water cooling or gas cooling or othersimilar methods.

Such distributed power density allows utilization of various hardmasking (e.g., resist) materials that may not have been consideredbefore with diffusion (high temperature) and directed implant (highinstantaneous power density).

Another advantage of the present invention is that no subsequentdiffusion is required, and thus, lower temperature anneal as low as 500°C. can provide enough activation and damage anneal that can be used forfabrication of a PV cell. Plasma grid implantation, due to its highproductivity, can provide higher doses. Therefore, if only a portion ofthe dopant is activated, the desired resistivity and performance canstill be achieved. Auto-annealing also may be employed, where the powerof the beam is used to heat the substrate to such a desired temperatureso that self-annealing can take place. Furthermore, balancing theelevated temperature of the substrate, masks, and grid assembly can beof major benefit in the general operation, control and metrology of thesystem.

Utilizing the high productivity of the unique plasma grid implantsystem, an integrated module of SiNx deposition in conjuction withjunction-doping applications can be also achieved without breaking thevacuum. The plasma grid implantation system of the present invention canbe used to achieve surface passivation. The difference betweenimplantation and deposition is the energy of the ions. The lower theenergy, the more the ions stay on the surface. The present inventionenables the formation of a passivation layer, such as a nitride film, onthe surface of the wafer through the use of a very low energy implant.The technique currently used is a chemical process. The presentinvention allows for the application of a passivation layer simply bybleeding a passivation gas, such as silicon or nitrogen, into the plasmaregion of the chamber.

FIG. 14 illustrates a process flow diagram of one embodiment of a method1400 of ion implantation in accordance with the principles of thepresent invention. At step 1410, a plasma is provided within a plasmaregion of a chamber. A first grid plate and a second grid plate aredisposed within the chamber. At step 1420, the second grid plate isnegatively biased. The second grid plate comprises a plurality ofapertures and is disposed in a first position. At step 1430, the firstgrid plate is positively biased. The first grid plate comprises aplurality of apertures and is disposed in a first position. AlthoughFIG. 14 shows the step of the second grid plate being negatively biasedbefore the step of the first grid plate being positively biased, in someembodiments, the biasing of the first grid plate is initiated before orsimultaneously with the biasing of the second grid plate. At step 1440,ions from the plasma in the plasma region are flown through theapertures in the positively-biased first grid plate. At step 1450, atleast a portion of the ions that flowed through the apertures in thepositively-biased first grid plate are flown through the apertures inthe negatively-biased second grid plate. At step 1460, a substrate isimplanted with at least a portion of the ions that flowed through theapertures in the negatively-biased second grid plate, with the substratebeing disposed in a first position. The process can then be repeatedwith the positioning of the grid plates and/or the substrate beingadjusted in order to achieve both homogeneous and selective ionimplantation.

FIG. 15 illustrates a process flow diagram of another embodiment of amethod 1500 of ion implantation in accordance with the principles of thepresent invention. At step 1510, a plasma is provided within a plasmaregion of a chamber. At step 1520, a grid assembly is providedcomprising a plurality of grid plates. Each grid plate comprises aplurality of apertures. At step 1530, a first set of ions from theplasma in the plasma region is flown through the apertures in each ofthe grid plates in the grid assembly while each of the grid plates is ina first position. At step 1540, a substrate is homogeneously implantedwith at least a portion of the first set of ions that flowed through theapertures in the grid plates while the substrate is supported in a firstposition by a substrate holder, thereby forming a singlelaterally-homogeneous ion implantation across the substrate from acombination of the first set of ions that have passed through differentapertures of the same grid plate. At step 1550, the position of thesubstrate or at least one of the grid plates is adjusted to a secondposition. At step 1560, a second set of ions from the plasma in theplasma region is flown through the apertures in each of the grid platesin the grid assembly subsequent to the adjustment to the secondposition. At step 1570, the substrate is selectively implanted with atleast a portion of the second set of ions that flowed through theapertures in the grid plates subsequent to the adjustment to the secondposition, thereby forming a plurality of laterally spaced-apart ionimplantations on the substrate from a portion of the second set of ionsthat have passed through different apertures of the same grid plate.

FIG. 16 illustrates a process flow diagram of yet another embodiment ofa method 1600 of ion implantation in accordance with the principles ofthe present invention. At step 1610, a single type of dopant material isprovided to a plasma generator. At step 1620, the plasma generatorbreaks up the single type of dopant material into a plurality of dopantspecies. At step 1630, a substrate is implanted with the plurality ofdopant species.

In some embodiments, a combination of different types of dopant materialis used to implant different pluralities of dopant species. In someembodiments, the different types of dopant material can be provided inprecursor form as gasses, liquids, solids, or any combination thereof.

The present invention has been described in terms of specificembodiments incorporating details to facilitate the understanding ofprinciples of construction and operation of the invention. Suchreference herein to specific embodiments and details thereof is notintended to limit the scope of the claims appended hereto. It will bereadily apparent to one skilled in the art that other variousmodifications may be made in the embodiment chosen for illustrationwithout departing from the spirit and scope of the invention as definedby the claims.

1. A plasma grid implantation system comprising: a plasma sourceconfigured to provide plasma; a first grid plate comprising a pluralityof apertures configured to allow ions from the plasma in a plasma regionto pass therethrough, wherein the first grid plate is configured to bepositively biased by a power supply; a second grid plate comprising aplurality of apertures configured to allow the ions to pass therethroughsubsequent to the ions passing through the first grid plate, wherein thesecond grid plate is configured to be negatively biased by a powersupply; and a substrate holder configured to support a substrate in aposition where the substrate is implanted with the ions subsequent tothe ions passing through the second grid plate.
 2. The system of claim1, wherein: the first grid plate is positively biased by a power supply;and the second grid plate is negatively biased by a power supply.
 3. Thesystem of claim 1, wherein: the position of at least one of the firstgrid plate, the second grid plate, and the substrate holder isconfigured to be adjusted between a homogeneous implantation positionand a selective implantation position; the homogeneous implantationposition is configured to enable a single laterally-homogeneous ionimplantation across the substrate on the substrate holder, wherein thesingle laterally-homogeneous ion implantation is formed from acombination of ions that have passed through different apertures of thesecond grid plate; and the selective implantation position is configuredto enable a plurality of laterally spaced-apart ion implantations of thesubstrate on the substrate holder, wherein the plurality of laterallyspaced-apart ion implantations is formed from ions that have passedthrough the different apertures of the second grid plate.
 4. The systemof claim 1, further comprising a third grid plate disposed between thesecond grid plate and the substrate holder, the third grid platecomprising a plurality of apertures configured to allow the ions to passtherethrough subsequent to the ions passing through the second gridplate.
 5. The system of claim 4, wherein the third grid plate isgrounded.
 6. The system of claim 4, wherein: the position of at leastone of the third grid plate and the substrate holder is configured to beadjusted between a homogeneous implantation position and a selectiveimplantation position; the homogeneous implantation position configuredto enable a single laterally-homogeneous ion implantation across thesubstrate on the substrate holder, wherein the singlelaterally-homogeneous ion implantation is formed from a combination ofions that have passed through different apertures of the second gridplate; and the selective implantation position configured to enable aplurality of laterally spaced-apart ion implantations of the substrateon the substrate holder, wherein the plurality of laterally spaced-apartion implantations is formed from ions that have passed through thedifferent apertures of the second grid plate.
 7. The system of claim 1,wherein the apertures of at least one of the first grid plate and thesecond grid plate are substantially circular holes.
 8. The system ofclaim 1, wherein the apertures of at least one of the first grid plateand the second grid plate are elongated slots.
 9. The system of claim 1,wherein each one of the apertures of at least one of the first gridplate and the second grid plate comprises a top end and a bottom end,wherein the bottom end is closer to the substrate holder than the topend, and wherein the diameter of each aperture gradually increases fromthe top end to the bottom end.
 10. The system of claim 1, wherein thefirst grid plate and the second grid plate comprise a material chosenfrom the group consisting of: silicon, graphite, silicon carbide, andtungsten.
 11. The system of claim 1, further comprising a chamberdefined by chamber walls, wherein the plasma region, the first gridplate, and the second grid plate are housed within the chamber, andwherein the chamber walls are configured to repel ions in the plasmaregion using an electric field.
 12. The system of claim 11, wherein oneor more magnets are coupled to the chamber walls.
 13. A method of ionimplantation comprising: providing a plasma within a plasma region of achamber; positively biasing a first grid plate, wherein the first gridplate comprises a plurality of apertures and is disposed in a firstposition; negatively biasing a second grid plate, wherein the secondgrid plate comprises a plurality of apertures and is disposed in a firstposition; flowing ions from the plasma in the plasma region through theapertures in the positively-biased first grid plate; flowing at least aportion of the ions that flowed through the apertures in thepositively-biased first grid plate through the apertures in thenegatively-biased second grid plate; and implanting a substrate with atleast a portion of the ions that flowed through the apertures in thenegatively-biased second grid plate, wherein the substrate is disposedin a first position.
 14. The method of claim 13, wherein a shadow maskcomprising a plurality of openings formed therethrough is disposed apredetermined distance away from the substrate, and the method furthercomprises: flowing at least a portion of the ions that flowed throughthe apertures in the negatively-biased second grid plate through theopenings in the shadow mask before implanting the substrate.
 15. Themethod of claim 13, wherein a photoresist mask comprising a plurality ofopenings formed therethrough is placed in contact with the substrate,and the method further comprises: flowing at least a portion of the ionsthat flowed through the apertures in the negatively-biased second gridplate through the openings in the photoresist mask before implanting thesubstrate.
 16. The method of claim 13, further comprising: adjusting theposition of at least one of the first grid plate, second grid plate, andthe substrate holder to a second position; providing a plasma within theplasma region subsequent to the adjustment to the second position;flowing ions from the plasma in the plasma region through the aperturesin the positively-biased first grid plate subsequent to adjustment tothe second position; flowing at least a portion of the ions that flowedthrough the apertures in the positively-biased first grid plate throughthe apertures in the negatively-biased second grid plate subsequent toadjustment to the second position; and implanting a substrate with atleast a portion of the ions that flowed through the apertures in thenegatively-biased second grid plate subsequent to adjustment to thesecond position, wherein the implantation performed when the at leastone of the first grid plate, second grid plate, and the substrate holderwas in the first position forms a single laterally-homogeneous ionimplantation across the substrate, wherein the singlelaterally-homogeneous ion implantation is formed from a combination ofions that have passed through different apertures of the second gridplate, and wherein the implantation performed when the at least one ofthe first grid plate, second grid plate, and the substrate holder was inthe second position forms a plurality of laterally spaced-apart ionimplantations of the substrate, wherein the plurality of laterallyspaced-apart ion implantations is formed from ions that have passedthrough the different apertures of the second grid plate.
 17. The methodof claim 13, wherein a third grid plate is disposed between the secondgrid plate and the substrate, the third grid plate disposed in a firstposition and comprising a plurality of apertures configured to allow theions to pass therethrough subsequent to the ions passing through thesecond grid plate.
 18. The system of claim 17, wherein the third gridplate is grounded.
 19. The method of claim 17, further comprising:adjusting the position of at least one of the first grid plate, secondgrid plate, the third grid plate, and the substrate holder to a secondposition; providing a plasma within the plasma region subsequent to theadjustment to the second position; flowing ions from the plasma in theplasma region through the apertures in the positively-biased first gridplate subsequent to adjustment to the second position; flowing at leasta portion of the ions that flowed through the apertures in thepositively-biased first grid plate through the apertures in thenegatively-biased second grid plate subsequent to adjustment to thesecond position; flowing at least a portion of the ions that flowedthrough the apertures in the negatively-biased second grid plate throughthe apertures in the third grid plate subsequent to adjustment to thesecond position; and implanting a substrate with at least a portion ofthe ions that flowed through the apertures in the third grid platesubsequent to adjustment to the second position, wherein theimplantation performed when the at least one of the first grid plate,second grid plate, the third grid plate, and the substrate holder was inthe first position forms a single laterally-homogeneous ion implantationacross the substrate, wherein the single laterally-homogeneous ionimplantation is formed from a combination of ions that have passedthrough different apertures of the third grid plate, and wherein theimplantation performed when the at least one of the first grid plate,second grid plate, the third grid plate, and the substrate holder was inthe second position forms a plurality of laterally spaced-apart ionimplantations of the substrate, wherein the plurality of laterallyspaced-apart ion implantations is formed from ions that have passedthrough the different apertures of the third grid plate.
 20. The methodof claim 13, wherein the apertures of at least one of the first gridplate and the second grid plate are substantially circular holes. 21.The method of claim 13, wherein the apertures of at least one of thefirst grid plate and the second grid plate are elongated slots.
 22. Themethod of claim 13, wherein each one of the apertures of at least one ofthe first grid plate and the second grid plate comprises a top end and abottom end, wherein the bottom end is closer to the substrate holderthan the top end, and wherein the diameter of each aperture graduallyincreases from the top end to the bottom end.
 23. The method of claim13, wherein the first grid plate and the second grid plate comprise amaterial chosen from the group consisting of: silicon, graphite, siliconcarbide, and tungsten.
 24. The method of claim 13, wherein the plasmaregion, the first grid plate, and the second grid plate are housedwithin a chamber that is defined by chamber walls, and wherein thechamber walls are configured to repel ions in the plasma region using anelectric field.
 25. The method of claim 13, further comprising the stepof applying a pulsed voltage to the plasma.
 26. The method of claim 13,further comprising the step of applying a pulsed voltage to thesubstrate.
 27. The method of claim 26, wherein the pulsed voltage isdirected towards a plurality of different locations on the substrate.28. The method of claim 13, further comprising: passing the substratethrough a first plurality of differentially-pumped stages prior to thesubstrate being implanted with the ions, wherein each stage in the firstplurality of differentially-pumped stages comprises a lower pressurethan the previous stage in the first plurality of differentially-pumpedstages; passing the substrate from the first plurality ofdifferentially-pumped stages directly to an implantation stage; passingthe substrate from the implantation stage directly to a second pluralityof differentially-pumped stages subsequent to the substrate beingimplanted with the ions, and passing the substrate through the secondplurality of differentially-pumped stages, wherein each stage in thesecond plurality of differentially-pumped stages comprises a higherpressure than the previous stage in the second plurality ofdifferentially-pumped stages, wherein the implantation stage comprises alower pressure than any of the stages in the first plurality and secondplurality of differentially-pumped stages.
 29. A plasma gridimplantation system comprising: a plasma source configured to provideplasma; a grid assembly comprising a plurality of grid plates, whereineach grid plate comprises a plurality of apertures configured to allowions from the plasma to pass therethrough; and a substrate holderconfigured to support a substrate in a position where the substrate isimplanted with the ions subsequent to the ions passing through theplurality of apertures of the grid plates, wherein at least one of thesubstrate holder and the grid plates is configured to be adjustedbetween a homogeneous implantation position and a selective implantationposition, wherein the homogeneous implantation position is configured toenable a single laterally-homogeneous ion implantation across thesubstrate on the substrate holder, the single laterally-homogeneous ionimplantation being formed from a combination of ions that have passedthrough different apertures of the second grid plate, and wherein theselective implantation position is configured to enable a plurality oflaterally spaced-apart ion implantations of the substrate on thesubstrate holder, the plurality of laterally spaced-apart ionimplantations being formed from ions that have passed through thedifferent apertures of the second grid plate.
 30. The system of claim29, wherein the plurality of grid plates comprises: a first grid platecomprising a plurality of apertures configured to allow ions from theplasma in a plasma region to pass therethrough; and a second grid platecomprising a plurality of apertures configured to allow the ions to passtherethrough subsequent to the ions passing through the first gridplate.
 31. The system of claim 30, wherein the first grid plate isconfigured to be positively-biased, either continuously in DC mode or inpulsed mode, by a power supply.
 32. The system of claim 31, wherein thesecond grid plate is configured to be negatively-biased, eithercontinuously in DC mode or in pulsed mode, by a power supply.
 33. Thesystem of claim 32, wherein the plurality of grid plates furthercomprises a third grid plate comprising a plurality of aperturesconfigured to allow the ions to pass therethrough subsequent to the ionspassing through the second grid plate.
 34. The system of claim 33,wherein the third grid plate is configured to be grounded.
 35. Thesystem of claim 30, wherein the first grid plate, the second grid plate,and the substrate holder are all configured to have their positionsadjusted.
 36. A method of ion implantation comprising: providing aplasma within a plasma region of a chamber; providing a grid assemblycomprising a plurality of grid plates, wherein each grid plate comprisesa plurality of apertures; flowing a first set of ions from the plasma inthe plasma region through the apertures in each of the grid plates inthe grid assembly while each of the grid plates is in a first position;homogeneously implanting a substrate with at least a portion of thefirst set of ions that flowed through the apertures in the grid plateswhile the substrate is supported in a first position by a substrateholder, thereby forming a single laterally-homogeneous ion implantationacross the substrate from a combination of the first set of ions thathave passed through different apertures of the same grid plate;adjusting the position of the substrate or at least one of the gridplates to a second position; flowing a second set of ions from theplasma in the plasma region through the apertures in each of the gridplates in the grid assembly subsequent to the adjustment to the secondposition; selectively implanting the substrate with at least a portionof the second set of ions that flowed through the apertures in the gridplates subsequent to the adjustment to the second position, therebyforming a plurality of laterally spaced-apart ion implantations on thesubstrate from a portion of the second set of ions that have passedthrough different apertures of the same grid plate.
 37. The method ofclaim 36, wherein the adjusting step comprises adjusting the position ofthe substrate.
 38. The method of claim 37, wherein adjusting theposition of the substrate comprises moving the substrate closer to thegrid assembly.
 39. The method of claim 36, wherein the adjusting stepcomprises adjusting the position of one of the grid plates.
 40. Themethod of claim 39, wherein adjusting the position of one of the gridplates comprises moving one of the grid plates closer to the substrate.41. The method of claim 36, wherein the plurality of grid platescomprises a first grid plate and a second grid plate, the first gridplate being positively-biased, and the second grid plate beingnegatively biased.
 42. The method of claim 41, wherein the plurality ofgrid plates further comprises a third grid plate that is grounded.
 43. Amethod of ion implantation comprising: providing a first single type ofdopant material to a plasma generator; the plasma generator breaking upthe first single type of dopant material into a first plurality ofdopant species; and implanting a substrate with the first plurality ofdopant species.
 44. The method of claim 43, wherein the substrate isimplanted with the first plurality of dopant species in a singleimplantation step.
 45. The method of claim 43, wherein each one of thedopant species is implanted into the substrate at a different depth. 46.The method of claim 43, wherein the first single type of dopant materialis phosphine.
 47. The method of claim 46, wherein the first plurality ofdopant species comprises P⁺, P⁺⁺, P⁺⁺⁺, P₂ ⁺, P₃ ⁺, and P₅ ⁺.
 48. Themethod of claim 43, wherein the first single type of dopant material isboron or arsenic.
 49. The method of claim 43, wherein: a second singletype of dopant material is provided to the plasma generator; the plasmagenerator breaks up the second single type of dopant material into asecond plurality of dopant species during the same period that theplasma generator breaks up the first single type of dopant material intothe first plurality of dopant species; and the second plurality ofdopant species is implanted into the substrate during the same periodthat the first plurality of dopant species is implanted into thesubstrate.
 50. The method of claim 49, wherein the first single type ofdopant material and the second single type of dopant material are each aprecursor gas.
 51. The method of claim 50, wherein the first single typeof dopant material is arsine and the second single type of dopantmaterial is phosphine.